Thread: ? warning message: ncompatible implicit declaration...

hi,

a program i have compiles fine, but in both OS X 10.4.10 and Fedora 6 i get the following warning:

incompatible implicit declaration of built-in function 'exit'

the only libraries are <stdio.h> and <string.h>.

just wondering if anyone has a clue what this might mean. here's an ex. of code that produces the error:

Code:

	if (something)			
	{
		printf("Blah\n");
		exit(1);
	}

thanks for any help!

p.s: new to C, coming from perl, ruby & javascript (obviously not compiled :-) )

How about including <stdlib.h>, which is where exit is actually prototyped.

Originally Posted by Govalant

you need to include stdlib.

maybe in some other compiler it included it automaticaly.

In fact you don't "need" to include it (but i don't mean in any way that you shouldn't include it).

If you do not include it, when your compiler will "compile" your source code, he won't be able to check if the function call you are making have the right argument type (which can lead to runtime errors if there's a need for conversion from a type to another) and enough argument (example, by not including stdlib.h, you could write something like exit(1, 1) and the program will compile fine, only giving you a warning). Also, it'll assume that every function not declared are returning int.

Not including header files shouldn't lead to compilation error. It could lead to runtime error tough.

If you don't believe me, try it. Write something silly like

Code:

int main()
{
	float fl;

	fl = (float) exit(1, 1);

	return 0;
}

...but i couldn't tell what will happen at runtime.